This invention relates to hammer assemblies and, more particularly, to hammer assemblies of the type including a housing having opposing open ends and an internal passage extending between the open ends, a hammer element positioned in the housing for reciprocal movement in the passage between first and second positions, and a biasing member coupled to the hammer element for biasing the hammer element in a desired direction relative to said first and second positions.
Hammer assemblies of the above-type have come into widespread commercial use in machines requiring high speed precision impacting of a desired object to be struck. An example is a high speed serial printer of the type employing a rotatable print wheel having a plurality of character elements extending radially from a central hub. In such printers, the print wheel is rotated until a character element desired for printing reaches a predetermined printing position. Then, the hammer assembly is activated to cause the hammer element thereof to strike the character element causing the imprinting of the character element on a desired recording medium.
U.S. Pat. No. 3,266,419 discloses a hammer assembly used in a serial printer employing a print wheel of the type having character elements formed about its peripheral surface, and U.S. application Ser. No. 505,105 filed on Sept. 11, 1974 in the name of Andrew Gabor and assigned to the assignee of the present invention discloses another hammer assembly used in a serial printer employing a "daisy wheel" type of print wheel where the character elements are formed on spokes projecting outwardly from a central hub.
In each of the above assemblies, the spring member used to hold the hammer element in a retracted position is disposed about the exterior of the hammer element. Not only does this increase the size requirements of the housing, but it also makes assembly difficult and cumbersome. In addition, and in the case of the hammer assembly of U.S. Pat. No. 3,266,419 where the spring member is in direct contact with the hammer element, should the hammer element be metallic like the spring member, corrosion due to prolonged frictional contact can occur.
In the case of hammer assemblies comprised of all metallic components, it is generally necessary to add a lubricant on a regular basis to reduce frictional resistance to movement of the hammer element in the housing, as well as to reduce the likelihood of corrosion. However, the lubricant has a tendency to collect dirt which can clog up the passage in which the hammer is disposed thereby hampering effective operation. Substantial clogging can retard the exhaust of air during reciprocal movement of the hammer element thereby resulting in a "piston effect" which can all but eliminate effective operation.
Certain hammer assemblies, such as the one disclosed in the aforementioned U.S. application Ser. No. 505,105, suffer from another deficiency, i.e. the impacting surface area of the hammer tip is not large enough to cover the full spread of character elements. This deficiency, the potential problems it engendures and a desired solution thereto are disclosed in the aforementioned U.S. application Ser. No. 606,981. Generally speaking, the desired solution resides in the provision of a "taller" hammer element having a specifically configured hammer tip. With such a taller hammer, it is clear that if the spring member continued to be disposed about the exterior of the hammer element, it would have to be of substantially larger size than that employed in the hammer assembly disclosed in U.S. application Ser. No. 505,105, thereby significantly reducing its effectiveness and adding to the overall size and cost of the assembly.
It would be desirable, therefore, to utilize the hammer element disclosed in the aforementioned U.S. application Ser. No. 606,981 in a hammer assembly where the various disadvantages and drawbacks of the prior art hammer assemblies discussed above would be substantially reduced or eliminated.